Table 2.

Oral contraceptive use and risk of breast cancera

All women (age 20–44)Age 20–39Age 40–44
ControlsCasesControlsCasesControlsCases
(n = 882)(n = 985)(n = 355)(n = 374)(n = 527)(n = 611)
n (%)n (%)ORb95% CIn (%)n (%)ORb95% CIn (%)n (%)ORb95% CI
Lifetime duration of use
 Never103 (11.7)119 (12.1)1.0(ref)44 (12.4)45 (12.0)1.0(ref)59 (11.2)74 (12.1)1.0(ref)
 Ever779 (88.3)866 (87.9)1.0(0.7–1.3)311 (87.6)329 (88.0)1.0(0.7–1.7)468 (88.8)537 (87.9)0.9(0.6–1.4)
  <5 years280 (31.8)306 (31.2)1.0(0.7–1.3)115 (32.4)107 (28.8)0.9(0.5–1.5)165 (31.4)199 (32.6)1.0(0.6–1.5)
  5–9.9 years219 (24.9)213 (21.7)0.9(0.6–1.2)86 (24.2)88 (23.7)1.1(0.6–1.8)133 (25.3)125 (20.5)0.7(0.5–1.2)
  10–14.9 years178 (20.2)169 (17.2)0.9(0.6–1.2)83 (23.4)80 (21.6)1.0(0.6–1.7)95 (18.1)89 (14.6)0.8(0.5–1.2)
  ≥15 years100 (11.4)174 (17.7)1.5(1.1–2.2)c27 (7.6)51 (13.7)1.9(1.0–3.7)73 (13.9)123 (20.2)1.4(0.9–2.2)
Time since last use (y)
 Current use144 (16.3)201 (20.4)1.3(0.9–1.8)72 (20.3)99 (26.5)1.4(0.8–2.4)72 (13.7)102 (16.7)1.1(0.7–1.8)
 Former use635 (72.0)665 (67.5)0.9(0.7–1.2)239 (67.3)230 (61.5)0.9(0.6–1.5)396 (75.1)435 (71.2)0.9(0.6–1.3)
  >1 to <5133 (15.1)132 (13.4)0.9(0.6–1.3)72 (20.3)73 (19.5)1.0(0.6–1.8)61 (11.6)59 (9.7)0.8(0.5–1.3)
  5–9.9161 (18.3)186 (18.9)1.0(0.7–1.4)72 (20.3)76 (20.3)1.0(0.6–1.8)89 (16.9)110 (18.0)1.0(0.6–1.6)
  10–14.9151 (17.1)133 (13.5)0.8(0.5–1.1)56 (15.8)48 (12.8)0.8(0.4–1.5)95 (18.0)85 (13.9)0.7(0.5–1.2)
  ≥15190 (21.5)214 (21.7)0.9(0.7–1.3)39 (11.0)33 (8.8)0.7(0.4–1.4)151 (28.7)181 (29.6)1.0(0.6–1.5)
Age at first use (y)
 <18284 (32.2)323 (32.8)1.0(0.7–1.4)131 (36.9)138 (36.9)1.0(0.6–1.7)153 (29.0)185 (30.3)0.9(0.6–1.5)
 18–20279 (31.6)288 (29.2)0.9(0.7–1.3)106 (29.9)115 (30.7)1.1(0.7–1.9)173 (32.8)173 (28.3)0.8(0.5–1.2)
 ≥21216 (24.5)255 (25.9)1.0(0.7–1.4)74 (20.8)76 (20.3)1.0(0.6–1.7)142 (26.9)179 (29.3)1.0(0.7–1.5)
Duration of use in the prior 5 years among current users
 Current use
  <3 years31 (3.5)44 (4.5)1.3(0.7–2.2)21 (5.9)24 (6.4)1.1(0.6–2.4)10 (1.9)20 (3.3)1.4(0.6–3.3)
  3–4.9 years58 (6.6)60 (6.1)0.9(0.6–1.4)34 (9.6)32 (8.6)1.0(0.5–1.8)24 (4.6)28 (4.6)0.9(0.4–1.6)
  ≥5 years54 (6.1)97 (9.8)1.6(1.1–2.5)c17 (4.8)43 (11.5)2.5(1.2–5.1)c37 (7.0)54 (8.8)1.2(0.7–2.1)
Recency of use and lifetime duration of use
 Former use
  <15 years598 (68.0)585 (59.6)0.9(0.6–1.2)232 (65.4)213 (57.4)0.9(0.6–1.5)366 (69.7)372 (61.0)0.8(0.6–1.2)
  ≥15 years37 (4.2)80 (8.2)1.9(1.2–3.1)c7 (2.0)17 (4.6)2.4(0.9–6.6)30 (5.7)63 (10.3)1.7(1.0–3.0)
 Current use
  <15 years79 (9.0)103 (10.5)1.2(0.8–1.8)52 (14.6)62 (16.7)1.2(0.7–2.2)27 (5.1)41 (6.7)1.2(0.6–2.1)
  ≥15 years63 (7.2)94 (9.6)1.3(0.9–2.0)20 (5.6)34 (9.2)1.7(0.8–3.4)43 (8.2)60 (9.8)1.1(0.7–1.9)

Abbreviations: OC, oral contraceptive; OR, odds ratio; CI, confidence interval.

  • aEver use is defined as OC use for ≥6 months and current use is defined as use of OCs within the prior year. Women who used OCs for <6 months (52 controls, 64 cases), only used progestin-only OC pills (7 controls, 5 cases), and with unknown OC use (2 controls, 2 cases) are excluded from all analyses. The reference group for all models is women who never used OCs.

  • bORs are adjusted for age, year, and race/ethnicity.

  • cP < 0.05.